<?php
    require_once PHPEXCEL_ROOT . 'PHPExcel/Shared/trend/linearBestFitClass.php';
    require_once PHPEXCEL_ROOT . 'PHPExcel/Shared/trend/logarithmicBestFitClass.php';
    require_once PHPEXCEL_ROOT . 'PHPExcel/Shared/trend/exponentialBestFitClass.php';
    require_once PHPEXCEL_ROOT . 'PHPExcel/Shared/trend/powerBestFitClass.php';
    require_once PHPEXCEL_ROOT . 'PHPExcel/Shared/trend/polynomialBestFitClass.php';

    /**
     * PHPExcel_trendClass
     * Copyright (c) 2006 - 2015 PHPExcel
     * This library is free software; you can redistribute it and/or
     * modify it under the terms of the GNU Lesser General Public
     * License as published by the Free Software Foundation; either
     * version 2.1 of the License, or (at your option) any later version.
     * This library is distributed in the hope that it will be useful,
     * but WITHOUT ANY WARRANTY; without even the implied warranty of
     * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     * Lesser General Public License for more details.
     * You should have received a copy of the GNU Lesser General Public
     * License along with this library; if not, write to the Free Software
     * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
     * @category   PHPExcel
     * @package    PHPExcel_Shared_Trend
     * @copyright  Copyright (c) 2006 - 2015 PHPExcel (http://www.codeplex.com/PHPExcel)
     * @license    http://www.gnu.org/licenses/old-licenses/lgpl-2.1.txt    LGPL
     * @version    ##VERSION##, ##DATE##
     */
    class trendClass {
        const TREND_LINEAR           = 'Linear';
        const TREND_LOGARITHMIC      = 'Logarithmic';
        const TREND_EXPONENTIAL      = 'Exponential';
        const TREND_POWER            = 'Power';
        const TREND_POLYNOMIAL_2     = 'Polynomial_2';
        const TREND_POLYNOMIAL_3     = 'Polynomial_3';
        const TREND_POLYNOMIAL_4     = 'Polynomial_4';
        const TREND_POLYNOMIAL_5     = 'Polynomial_5';
        const TREND_POLYNOMIAL_6     = 'Polynomial_6';
        const TREND_BEST_FIT         = 'Bestfit';
        const TREND_BEST_FIT_NO_POLY = 'Bestfit_no_Polynomials';
        /**
         * Names of the best-fit trend analysis methods
         * @var string[]
         **/
        private static $trendTypes = [
            self::TREND_LINEAR,
            self::TREND_LOGARITHMIC,
            self::TREND_EXPONENTIAL,
            self::TREND_POWER
        ];
        /**
         * Names of the best-fit trend polynomial orders
         * @var string[]
         **/
        private static $trendTypePolynomialOrders = [
            self::TREND_POLYNOMIAL_2,
            self::TREND_POLYNOMIAL_3,
            self::TREND_POLYNOMIAL_4,
            self::TREND_POLYNOMIAL_5,
            self::TREND_POLYNOMIAL_6
        ];
        /**
         * Cached results for each method when trying to identify which provides the best fit
         * @var PHPExcel_Best_Fit[]
         **/
        private static $trendCache = [];

        public static function calculate($trendType = self::TREND_BEST_FIT, $yValues, $xValues = [], $const = true) {
            //    Calculate number of points in each dataset
            $nY = count($yValues);
            $nX = count($xValues);
            //    Define X Values if necessary
            if ($nX == 0) {
                $xValues = range(1, $nY);
                $nX      = $nY;
            } elseif ($nY != $nX) {
                //    Ensure both arrays of points are the same size
                trigger_error("trend(): Number of elements in coordinate arrays do not match.", E_USER_ERROR);
            }
            $key = md5($trendType . $const . serialize($yValues) . serialize($xValues));
            //    Determine which trend method has been requested
            switch ($trendType) {
                //    Instantiate and return the class for the requested trend method
                case self::TREND_LINEAR:
                case self::TREND_LOGARITHMIC:
                case self::TREND_EXPONENTIAL:
                case self::TREND_POWER:
                    if (!isset(self::$trendCache[$key])) {
                        $className              = 'PHPExcel_' . $trendType . '_Best_Fit';
                        self::$trendCache[$key] = new $className($yValues, $xValues, $const);
                    }
                    return self::$trendCache[$key];
                case self::TREND_POLYNOMIAL_2:
                case self::TREND_POLYNOMIAL_3:
                case self::TREND_POLYNOMIAL_4:
                case self::TREND_POLYNOMIAL_5:
                case self::TREND_POLYNOMIAL_6:
                    if (!isset(self::$trendCache[$key])) {
                        $order                  = substr($trendType, -1);
                        self::$trendCache[$key] = new PHPExcel_Polynomial_Best_Fit($order, $yValues, $xValues, $const);
                    }
                    return self::$trendCache[$key];
                case self::TREND_BEST_FIT:
                case self::TREND_BEST_FIT_NO_POLY:
                    //    If the request is to determine the best fit regression, then we test each trend line in turn
                    //    Start by generating an instance of each available trend method
                    foreach (self::$trendTypes as $trendMethod) {
                        $className                  = 'PHPExcel_' . $trendMethod . 'BestFit';
                        $bestFit[$trendMethod]      = new $className($yValues, $xValues, $const);
                        $bestFitValue[$trendMethod] = $bestFit[$trendMethod]->getGoodnessOfFit();
                    }
                    if ($trendType != self::TREND_BEST_FIT_NO_POLY) {
                        foreach (self::$trendTypePolynomialOrders as $trendMethod) {
                            $order                 = substr($trendMethod, -1);
                            $bestFit[$trendMethod] = new PHPExcel_Polynomial_Best_Fit($order, $yValues, $xValues, $const);
                            if ($bestFit[$trendMethod]->getError()) {
                                unset($bestFit[$trendMethod]);
                            } else {
                                $bestFitValue[$trendMethod] = $bestFit[$trendMethod]->getGoodnessOfFit();
                            }
                        }
                    }
                    //    Determine which of our trend lines is the best fit, and then we return the instance of that trend class
                    arsort($bestFitValue);
                    $bestFitType = key($bestFitValue);
                    return $bestFit[$bestFitType];
                default:
                    return false;
            }
        }
    }
